Generally, an air conditioner comprises an outdoor unit equipped with a compressor, an outdoor heat exchanger, a pressure reducing mechanism and the like, and an indoor unit equipped with an indoor heat exchanger. The outdoor unit and the indoor unit are connected to each other with connection piping comprising a gas pipe, a liquid pipe or the like, and thereby a refrigerant circuit is formed between the outdoor unit and the indoor unit. In such an air conditioner, the refrigerant is circulated in the refrigerant circuit by driving the compressor, and thereby heat absorbed by the outdoor heat exchanger is released by the indoor heat exchanger so that heating operation is performed, or thereby heat absorbed by the indoor heat exchanger is released by the outdoor heat exchanger so that cooling operation is performed.
In this air conditioner, heat is transferred by means of the refrigerant as shown above, and thereby air conditioning operation is enabled. Therefore, the rate of refrigerant circulation expressed in refrigerant weight flowing per unit time needs to be increased or decreased depending on the air conditioning power of the equipment. However, when the refrigerant circulation rate is increased, leaving the gas pipe thickness as it is without changes would cause pressure loss due to the gas pipe to increase so that the air conditioning power would lower. On this account, in this air conditioner, the diameter of the gas pipe is changed according to the refrigerant circulation rate. For example, when HCFC-22 conventionally in common use is used as the refrigerant, gas pipes having a diameter of about 12.7 mm (hereinafter, referred to as "4/8-dia. pipe") is used in middle-sized and large-sized air conditioners whose refrigerant circulation rate is about 100 kg/h (kilogram per hour, likewise hereinafter) or about 150 kg/h or so. In small-sized air conditioners whose refrigerant circulation rate is about 60 kg/h or about 80 kg/h or so, gas pipes having a diameter of about 9.5 mm (hereinafter, referred to as "3/8-dia. pipe") are used. That is, it is a normal mode of application with use of HCFC-22 as the refrigerant that, a 4/8-dia. pipe is used as the aforementioned gas pipe in middle-sized and large-sized air conditioners whose rated cooling power is not less than 4.0 kW as defined by "JIS C 9612" of Japanese Industrial Standards, while a 3/8-dia. pipe is used as the gas pipe in small-sized air conditioners whose rated cooling power is less than 4.0 kW. Then, by changing the diameter of the gas pipe according to the air conditioning power of the air conditioner, a reduction in pressure loss is implemented in the middle-sized and large-sized air conditioners, and construction work is facilitated in the small-sized air conditioners. Besides, a cost reduction is implemented. It is noted that the cooling power as defined by "JIS C 9612" of Japanese Industrial Standards refers to a "quantity of heat (kW) that is removed in unit time from indoors when a room air conditioner is cooling operated".
In recent years, a demand for cost reduction to air conditioners and a demand for improvement in workability have been increasing more and more. In particular, the 4/8-dia. pipes are difficult to bend by hand in installation, which makes a cause of hindering the improvement in workability. However, only making the gas pipe smaller in diameter would cause occurrence of a problem that the pressure loss in the refrigerant circuit increases with the result of lowered air conditioning power.
Meanwhile, since HCFC-22 conventionally used as the refrigerant has become a target of fluorine regulation, alternative refrigerants substituting for HCFC-22 have begun to be discussed in various ways. However, there has been provided no alternative refrigerant that shows physical property values equivalent to or higher than the refrigerant HCFC-22 in all the aspects. Accordingly, which alternative refrigerant is appropriate for use is now under discussions, depending on the purpose of use.